1. Field of the Invention
The present invention relates to an image processing system which is suitable for detection of foreign matter on surfaces of various types of window.
2. Description of Related Art
Droplets such as raindrops, fog and dust on surfaces of window glass used in vehicles, ships and aircraft or in ordinary buildings deteriorate the visibility of the window. A known solution to this problem is an image processing system which detects such foreign matter and removes it by various means.
Patent Literature 1 (JP-B No. 89099/1995) discloses a technique that window is illuminated by two light sources and reflected light from the window is detected by an imaging device and raindrops on the outer surface of the window and fog on its inner surface are evaluated according to the intensity of the reflected light. Patent Literature 2 (PC (WO) 2001-516670) discloses a technique of simplifying an image processing system that one light source and a lens are used to illuminate window and reflected light from the window is detected by an imaging device to evaluate foreign mater on the outer surface of the window. Patent Literature 3 (JP-A No. 160779/1999) describes a technique that a filter in front of an in-vehicle camera is moved in and out mechanically by a motor to capture images under a plurality of conditions to detect foreign matter on an outer surface of window.